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<a name="Standard-Libraries-1"></a>
<h3 class="section">14.5 Standard Libraries</h3>

<a name="index-Wall-1"></a>
<p>GCC by itself attempts to be a conforming freestanding implementation.
See <a href="Standards.html#Standards">Language Standards Supported by GCC</a>, for details of
what this means.  Beyond the library facilities required of such an
implementation, the rest of the C library is supplied by the vendor of
the operating system.  If that C library doesn&rsquo;t conform to the C
standards, then your programs might get warnings (especially when using
<samp>-Wall</samp>) that you don&rsquo;t expect.
</p>
<p>For example, the <code>sprintf</code> function on SunOS 4.1.3 returns
<code>char *</code> while the C standard says that <code>sprintf</code> returns an
<code>int</code>.  The <code>fixincludes</code> program could make the prototype for
this function match the Standard, but that would be wrong, since the
function will still return <code>char *</code>.
</p>
<p>If you need a Standard compliant library, then you need to find one, as
GCC does not provide one.  The GNU C library (called <code>glibc</code>)
provides ISO C, POSIX, BSD, SystemV and X/Open compatibility for
GNU/Linux and HURD-based GNU systems; no recent version of it supports
other systems, though some very old versions did.  Version 2.2 of the
GNU C library includes nearly complete C99 support.  You could also ask
your operating system vendor if newer libraries are available.
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